Isolation of differentially expressed genes by combining representational difference analysis (RDA) and cDNA library arrays.

The difference products (DP) of representational difference analyses (RDA) were used as hybridization probes on cDNA arrays. The effectivity of RDA products obtained with increasing driver/tester ratios (DP 1 = 100:1, DP 2 = 800:1 and DP 3 = 400,000:1) to isolate differentially expressed genes was compared with the effectivity of conventional differential hybridizations. Pacreatic cancer and control tissues were used as a test system to isolate differentially expressed genes. The use of RDA products as hybridization probes showed two major advantages: (i) a reliable identification of true differential signals; and (ii) only one autoradiograph had to be analyzed, which eliminated the need for a laborious subtraction of signal intensities obtained with different cDNA probes. Increasing driver/tester ratios in iterative rounds of RDA delivered more specific results, though the total yield of differential clones was gradually reduced. In this situation, the intermediate RDA product DP 2 provided the best compromise.